For context, there are two stray dogs at our local city park that we can’t outright adopt, apartment rules say no pets, but we’ve been doing our best within our means to care for them at the park in the meantime.
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Warm water will melt the sap.
You can try giving them a nice warm bath. I’m sure the dogs will enjoy that. You can use the opportunity to wash them with flea/tick shampoo at the same time.
You may not be able to keep pets in your apartment, but that doesn’t mean you can’t bring them in for a brief while in order to bathe them.